We continue to concentrate on hemopoietic defects and single-gene induced mouse anemias, and to serve as a research resource for these and other mutants affecting development and function. Special attention will be given to preservation of 95 unique genetic stocks. Many techniques, including in vitro culture of hemopoietic tissues, will be used to analyze the etiology of Hertwig's macrocytic anemia and to compare it with W/Wv and S1/S1d. Rapid phenotypic identification of heterozygous carriers of 4 hemolytic mutants will be used to facilitate linkage studies and to prepare multiple carrier stocks to test genetic load effects on susceptibility to toxic environmental agents. Genetic fine structure of the W-locus and its relation to pleiotropism will be investigated through analysis of 18 new W-alleles with diverse effects on hemopoiesis, germ cell development, and melanoblast distribution. We will try to determine whether W is a unitary locus or a complex chromosomal region.